This invention relates generally to conveyor systems and more particularly to conveyors of the type commonly known as power and free conveyors. Still more particularly, the invention relates to a mechanism for detaching the trolleys of power and free conveyors from the drive chain when the trolleys approach preceding carriers that are stopped on the conveyor track.
In automobile assembly plants and other applications, large conveyor systems are commonly used to convey articles such as partially completed automobile bodies between work stations arranged along the conveyor path. One type of conveyor system that has been popular in this type of application is known as a power and free conveyor. A power and flee conveyor includes a chain which is driven continuously along a track. The automobile bodies or other articles are conveyed on carriers which are mounted on wheeled trolleys riding on another track. The chain has spaced apart drive dogs that are detachably engaged with retractable dogs on the trolleys so that each trolley which has its retractable trolley dog engaged by a chain dog is driven along the conveyor path.
Power and free conveyors can be overhead systems where the load is suspended from the carrier. Alternatively, inverted power and free conveyors have the load on top of the carrier with the chain running beneath the trolleys and the chain dogs projecting upwardly.
Normally, a number of work stations are located along the conveyor where the carriers are stopped so that various types of operations can be performed on the work. Stop mechanisms have been developed for detaching the trolley dog from the chain dog in order to stop the carrier at the location of each work station. For example, retractable blades and cams can be installed at each work station and extend into the path of an approaching trolley. A pivot arm carrying the trolley dog is engaged by the stop device and pivoted in a direction to detach the trolley dog from the chain dog, thus stopping the trolley while the chain continues to move and convey other trolleys along the conveyor path.
Accumulation of carriers occurs in this type of conveyor system. If a carrier is stopped and the succeeding carrier approaches it, the incoming carrier must be stopped before it bangs into the stopped carrier and causes damage to the equipment and possibly to personnel in the vicinity. Accumulation devices of various types have been used to stop carriers which approach preceding carriers that are stationary. Usually, the trolley on the trailing end of each carrier is equipped with a cam surface which is engaged by the pivot arm of the trolley on the leading end of the succeeding carrier. When the pivot arm comes into contact with the cam surface, the trolley arm is pivoted to a retracted position wherein the trolley dog is released from the drive dog on the chain.
Accumulator mechanisms of this type are characterized by cost and complexity and have been plagued by other problems, particularly in the area of reliability. In order to function properly, the trailing cam surface must be located properly to intercept the incoming trolley arm. There is little tolerance for error, so if either part is bent up or down or sidewardly, or if the parts are misaligned slightly for some other reason, the pivot arm may not be retracted far enough to fully release the trolley dog from the chain dog, and serious adverse consequences can result. Conversely, the pivot arm may be subjected to over travel which can bend or break the arm or associated parts of the trolley. In either case, costly repairs must be made to the conveyor equipment, and it may be necessary to take the system out of production for an extended time while it is being repaired.
The present invention is directed to an improved accumulation device for a conveyor system which operates reliably to stop carriers which approach preceding carriers on the conveyor track. It is the principal goal of the invention to provide an accumulation mechanism which is specially constructed in a manner to function properly even if the cooperating parts are bent or otherwise deformed from their original condition.
More particularly, it is an object of the invention to provide an accumulation mechanism which is arranged to assure that the trolley arm is pivoted sufficiently to disengage the trolley dog from the chain dog while avoiding over travel of the pivot arm or other parts. Accordingly, the mechanism operates reliably within a wide range of tolerance and yet is not subjected to possible damage resulting from unintended over travel.
Another important object of the invention is to provide an accumulator mechanism of the character described which is well suited for addition to an existing trolley mechanism operated by a conventional stop device. This allows the existing stop mechanism to be used along with the mechanism of the present invention so that equipment modification and costs are minimized.
A further object of the invention is to provide an accumulator mechanism which is economical to manufacture and which is characterized by a sturdy construction.
These and other objects are achieved by the provision of an accumulator mechanism that includes an actuating lever pivotally mounted between a pair of side plates forming a rigid frame mounted on the trolley. A pivot plate is also pivotally mounted on the frame to turn on a pivot axis onset from the pivot axis for the actuating lever. A cam roller carried on the lever acts in a cam slot in the pivot plate. When the lever comes into contact with a preceding carrier on the conveyor path, the lever is pivoted to move the cam roller in the slot. The slot has a special configuration that causes the plate to pivot in a direction to raise a lifting link which is attached to the arm carrying the trolley dog. The lift link pulls the trolley arm in a direction to disengage the trolley dog from the drive dog on the chain.
The actuating lever has a plate that is located to come into engagement with the preceding carrier. The plate is long enough that some part of it will contact the carrier even if one or both parts are bent to a considerable extent. Consequently, the actuating lever will be actuated even if the parts are deformed.
It is a particular feature of the invention that the slot has a dual arc configuration. The slot configuration is such that an initial small increment of movement of the cam roller pivots the plate sufficiently that the trolley dog is completely disengaged. Further movement of the cam roller in the slot is essentially lost motion which has no effect on the pivot plate. Therefore if the actuating lever is pivoted beyond the range ot its normal movement, the cam roller simply moves idly in the slot and there is no over travel of any parts or binding that could break the mechanism. At the same time, the small increment of lever movement that is effective to disengage the trolley dog assures reliable disengagement even if the parts are deformed.